1. Field of the Invention
This invention relates to systems for detecting moving targets, and in particular to hose systems adapted for displaying the moving target in the manner capable of ready recognition thereof with respect to the field of view background.
2. Description of the Prior Art
In the prior art, there has arisen a need for systems capable of detecting the movement of an object within a defined field of view. For example, there are installations to be protected against the intrusion of unidentified persons. Similar systems have been developed to detect the presence or approach of moving airplanes.
In the prior art, systems have been developed utilizing a TV camera for observing a field of view for detecting the movement of an object or target therein. Typically, such systems apply frames of the video signal sensed at first and second points in time, to a suitable storage medium such as a magnetic disk recorder, whereby the first and second frames of the video signals may be subtracted from each other to provide a difference signal indicative of the movement of an object within the field of view. In such systems since the background within the field of view remains the same, these portions of the images are subtracted from each other and do not appear in the display. However, if an object within the field of view moves between frames or images, a difference signal is generated and is displayed, indicating that the object has moved.
A similar type of display may be achieved with direct view storage tubes, wherein the first frame of the video signal is stored upon a storage grid thereof and the second frame is applied to modulate a read electron beam, directed toward the storage grid whereon the first frame of information is stored. The stored first image modulates the read beam of electrons whereby the displayed image indicates the difference between the first and second frames. As a result, the object moving within the field of view is displayed upon the direct view storage tube.
Both of the above-described systems require the use of an expensive storage device such as a magnetic disk recorder or a direct view storage tube, and of additional complex circuitry for subtracting stored signals as in the case of the magnetic disk recorder, or timing circuitry whereby the video signals are applied in the desired sequence to the direct view storage tube.